1. Field of the Invention
A corrosion protection system for bridge stay cables.
2. Description of the Prior Art
The development of cable-stayed bridges has broadened the design and construction of bridges over bridge systems such as truss girders, arches and suspension bridges. Corrosion protection of the stay cables for cable-stayed bridges is essential to the durability and longevity of such bridges.
Typically the cables are protected by coating the strands or wires with a synthetic resin cover disposed within a tube and injection of a rust resistant solidifying filler such as cement into the tube surrounding the strands or wires.
U.S. Pat. No. 4,633,540 teaches a corrosion protection system for a stayed girder bridge including protection of the ends of the tensioning elements located in the anchorages by filling the space containing the protruding ends of the tension elements with the synthetic resin. As set forth in Column 2, lines 53 and 54, the invention is directed to " . . . , a temporary corrosion protection must be provided at the construction site." As shown in FIG. 2b of U.S. Pat. No. 4,633,540, the diagonal cable can be replaced when the space within the tubular sheathing 5 and the anchor tube 9' is filled with a nonhardenable corrosion protection material 6' such as grease.
U.S. Pat. No. 4,799,307 discloses an anchor apparatus which provides corrosion protection for the exposed cable in a region where the anchor body is attached to a tendon of a prestressed concrete slab. Fittings are provided for inserting corrosion resistant grease into interior cavities as a second line of corrosion protection.
U.S. Pat. No. 4,569,708 shows a method of fitting a corrosion protective sheath on a cable including the steps of fitting a sheath unit on one end of a cable, shifting the position of the fitted sheath unit toward the outer end of the cable, fitting a second sheath unit similarly on the cable in continuation from the preceding sheath unit and repeating the fitting of another sheath unit and the shift of the preceding sheath until the cable is covered with the sheath units substantially over the entire length thereof.
Unfortunately the solidifying fillers found in such systems expand and contract due to changes in temperature and are exposed to cyclic stress variations due to live loads, eventually causing the solidifying fillers to crack or flow and thereby reducing the effectiveness of the corrosion protection system.